

HDDs will draw around 4W idle each, 8W in total
Whether your drives are idle is also a very use-case specific thing and I wouldn’t spend any time trying to generalize based on that math as a “oh this is how it works for everyone”.
In my case, I’ve got 5 drives all spun up at all times because of torrrent clients, Jellyfin users, and just general media acquisition and public content serving.
This thing would dramatically reduce my power footprint and save me giant buckets of money over it’s lifespan while being smaller/faster IO performance/lower noise.
(My current nas sucks down about 120-140w 24/7, so…)
Anecdata, but SSDs will last longer than you want to use them in terms of write endurance.
My NAS OS SSDs are 500gb hynix drives from about 8 years ago, and they’re pushing 150 TBW.
150TB is a LOT of write cycles on a small drive, and they’re still reporting 94% endurance remaining.
The controller will die or I’ll upgrade well before that breaks at the rate it’s going.
Also keep in mind that you can read flash all you want and that doesn’t wear anything (unlike a HDD, amusingly), so for most consumer use cases, they’ll load the drive up with their data, and then only slowly modify or add to it, but have lots and lots of read access.